In secure communications systems, it is often required that a transmitted message synchronization preamble be non-determinable, non-spoof able and non-predictable. This is especially true for transmission security (TRANSEC) communications, the component of communications security (COMSEC) that results from the application of measures designed to protect transmissions from interception and exploitation by means other than cryptanalysis. Goals of TRANSEC include low probability of interception (LPI), low probability of detection (LPD) and anti-jam, or resistance to jamming. These requirements have led to the use of non-optimally orthogonal binary sequences generated by a pseudo random algorithm for synchronization preambles. To make up for the lack of orthogonality, longer lengths of preamble sequences must usually be transmitted to gain the same synchronization confidence and false alarm rate. However, transmitting longer lengths of preamble sequences generally requires increased transmit power and consumes time-bandwidth, producing less efficient resulting waveforms.
In military contexts, this increased transmit power and time-bandwidth consumption is particularly undesirable. For instance, in a battlefield situation, low transmit power is important for minimizing the likelihood of signal detection by hostile parties, thereby preventing the transmitter's position from being compromised. This may be especially true in a situation where a small team of radio-equipped personnel is located within a hostile region and must communicate with a distant device. For any single radio to communicate with the distant device, considerable transmit power is often required, resulting in a significant opportunity for detection by hostile forces. Moreover, the transmit power level required to communicate over significant distances would likely drain the radio's battery more rapidly than desired. As a result, a need exists to minimize RF emissions during preamble synchronization while maintaining robust, secure communication.
Consequently, a system and method for preprocessing transmission sequences in a jammed environment is necessary.